Liquids and gases have been stored in tanks for many years. When the liquid or gas is to be stored in the tank at a temperature substantially above or below ambient or atmospheric temperature, it is often necessary or at least highly desirable for tank penetrations to be located above the intended maximum stored product level so as to maintain structural integrity of the tank bottom and wall for safety reasons.
The configuration of pipe connections for carrying hot or cold fluids in or out through the roof of a tank is an important consideration. As a result, there is substantial variation in arrangements, sometimes due to roof configuration and whether the pipe terminates at the roof line, extends some distance inside the tank, or connects rigidly to an inner tank roof if one is present. In addition to the forces caused by the weight of the connection structural components, and the weight and dynamics of the flowing product, the design must consider the movement of the structural components due to temperature change. Also, when a large double walled tank is involved, for economic reasons the outer tank, outside of the boundaries of the tank insulation, is often made of material which is not resistant to the low or high temperature of the product. As a result, it is necessary to protect the tank roof from the temperature of the product.
In one type of roof connection an expansion bellows is incorporated in the transition between the hot or cold pipe and an ambient temperature outer roof. The function of the connection is to provide a continuous seal while permitting the required movement and yet maintain the intended temperature differential between the pipe and the roof. To maintain the temperature differential, it is necessary to add insulation between the bellows assembly and the pipe. The insulation has traditionally been installed from inside the tank roof before the tank goes into service. The insulation most commonly used has been a glass fiber blanket wrapped around the pipe and slid into the gap. To reduce convection and fill the space, the blanket is precompressed or packed into the space.
Problems have been encountered installing the insulation system on large pipe and connection sizes. As pipe sizes increased, visibility in the space decreased, reaching into the space became impossible and the force required to slide the insulation into place increased to the point where hand work became ineffective. If the insulation was not sufficiently precompressed and fastened during installation there was danger of it sliding down the pipe. In a tank for storing a cryogenic liquid, if voids were left in the insulation, frost or ice might appear on the outside of the bellows or distance piece or sleeve assembly adjacent to the voids. Whenever any problem of this type did appear, it was very difficult to make repairs because of lack of access.
From the above discussion it is believed clear that a need exists for alternative means of insulating a roof connection to a tank.